Nitrile Rubber (NBR)
One number defines this rubber. Acrylonitrile content sets oil resistance and low-temperature flexibility in opposite directions at the same time, and choosing it correctly is most of the specification work.
Molecular Structure
What is Nitrile Rubber (NBR)?
Nitrile rubber is a copolymer of butadiene and acrylonitrile made by emulsion polymerisation. The butadiene units provide chain flexibility and the double bonds that sulphur crosslinks; the acrylonitrile units contribute strongly polar nitrile groups. Those polar groups are the whole point — hydrocarbons are non-polar, and a polymer full of nitrile groups is thermodynamically unwilling to let them in.
Acrylonitrile content therefore governs oil resistance directly, and it runs from around 18% to 50% depending on grade. But it also raises the glass transition, from roughly −40 °C at low ACN to around −5 °C at high ACN. The two effects work against each other, and no grade gives both the best oil resistance and the best cold flexibility.
Two variants extend the range. Hydrogenated nitrile has its residual backbone double bonds hydrogenated away, which transforms heat and ozone resistance while keeping the oil resistance intact. Carboxylated nitrile adds carboxyl groups for much higher abrasion resistance and tensile strength, and is the basis of the disposable glove market.
Choose acrylonitrile content against the coldest temperature the part will see, not just the fluid it has to resist. A 50% ACN compound will outlast anything in hot oil and will be effectively rigid on a winter morning. Most failures traced back to grade selection are cold-start failures on a grade chosen purely for fluid resistance.
Quick Reference
Key Physical & Chemical Properties
Structure & Bonding
Butadiene units carrying in-chain double bonds, interrupted by acrylonitrile units bearing a pendant nitrile group. The nitriles are strongly polar and are what exclude hydrocarbons; the double bonds are the cure sites and also the weak point in ozone and heat.
Chain segment — pendant nitrile among butadiene unsaturation
Structural Identity
- PolymerNitrile butadiene rubber
- Composition(C₄H₆·C₃H₃N)ₙ
- ArrangementRandom copolymer, emulsion made
- Nitrile contributesOil resistance, hardness, higher Tg
- Butadiene contributesFlexibility and cure sites
- ACN range18 – 50%, the primary property lever
- Key trade-offOil resistance against cold flexibility
- HNBRBackbone double bonds hydrogenated
- XNBRCarboxylated — abrasion and gloves
- CAS Number9003-18-3
- Specified byACN content, Mooney, antioxidant
Product Specifications
Chelora supplies Nitrile Rubber (NBR) in standard and custom grades. Contact us for specification sheets tailored to your process.
| Polymer | Nitrile butadiene rubber |
|---|---|
| CAS Number | 9003-18-3 |
| Composition | (C₄H₆·C₃H₃N)ₙ |
| Acrylonitrile content | 18 – 50 wt%, declared per grade |
| Grade bands | Low ≤ 24%, medium 25 – 34%, high ≥ 35% |
| Mooney viscosity ML(1+4) 100 °C | 30 – 90, grade dependent |
| Volatile matter (max) | ≤ 0.75 wt% |
| Ash (max) | ≤ 1.5 wt% |
| Coagulant type | Calcium or magnesium — affects water resistance |
| Antioxidant type | Staining or non-staining — specify |
| Glass transition | −40 °C at 18% ACN to ≈ −5 °C at 50% ACN |
| Raw polymer density | 0.96 – 1.00 g/cm³, rises with ACN |
| Cure system | Sulphur / accelerator, or peroxide |
| Service temperature | −30 to +100 °C; HNBR to +150 °C |
| Oil resistance | Excellent — improves with ACN content |
| Ozone resistance | Poor — protect or select HNBR |
| Supply form | 35 kg bales; latex supplied separately |
| Packaging | Palletised or crated bales, 1000 – 1200 kg |
| Transport classification | Not regulated as dangerous goods |
Downstream Applications & Derivatives
Key derivative chains and industrial uses of Nitrile Rubber (NBR).
Oil Seals & O-Rings
The core application. Rotary shaft seals, O-rings, gaskets and diaphragms in contact with mineral oil, hydraulic fluid and grease — NBR is the default sealing elastomer.
Disposable Gloves
Carboxylated NBR latex gloves, now the standard in medical, laboratory and food handling after natural rubber latex protein allergy drove the switch.
Fuel & Hydraulic Hose
Inner liners for fuel, oil and hydraulic hose, where the nitrile resists the fluid and an outer cover of a weather-resistant rubber handles the environment.
Oilfield & HNBR
Hydrogenated grades for downhole packers, seals and stators, where oil resistance has to survive high temperature and sour service that standard NBR would not.
Rollers & Roll Covers
Printing, paper and textile rollers, and rice hulling rolls, where oil and solvent resistance combine with abrasion performance.
Moulded Industrial Goods
Bellows, grommets, mounts, cable glands and moulded parts throughout automotive and machinery, wherever a hydrocarbon fluid is present.
Why source Nitrile Rubber (NBR) through Chelora Petrochem?
Verified Origin
Full origin certification and asset-backed supply chain documentation — no grey-market supply or unlabelled reclaim.
Grade Flexibility
Low, medium and high acrylonitrile grades supplied, plus carboxylated and hydrogenated variants. We match on ACN content first, then Mooney, because that is the order in which the properties are actually decided.
Full Documentation
CoA covering ACN content, Mooney with test conditions, volatiles, ash and coagulant type; SDS; REACH compliance; and food-contact or medical documentation where the grade supports it.
Logistics Support
Experienced in bale rubber logistics — palletised and crated bales with film wrapping, containerised delivery with attention to stack height and temperature, for Indian and international delivery.
Storage & Handling Guidelines
Always refer to the full SDS before handling. The following is a summary of key requirements.
- Store cool, dry and out of direct sunlight, and limit stack height. Low-Mooney grades cold flow and knit together under sustained load.
- Keep bales away from electric motors, welding equipment and other ozone sources. NBR has backbone unsaturation and is genuinely ozone sensitive — stored bales develop surface cracking near ozone generators.
- Segregate grades by acrylonitrile content. Bales are indistinguishable by eye, and substituting a 33% grade for a 41% grade will change both oil swell and cold performance without any visible difference.
- Confirm the coagulant type where water resistance matters. Calcium-coagulated grades absorb less water than magnesium-coagulated ones, which matters for seals in wet or humid service.
- Specify antioxidant type up front. Staining antioxidants discolour light-coloured goods and migrate into adjacent materials, and the choice cannot be corrected after mixing.
- Design ozone protection into the compound or the part. NBR seals exposed to air under strain will crack, and antiozonant, a protective cover layer or a switch to HNBR are the available answers.
- Match acrylonitrile content to the lowest service temperature as well as the fluid. High ACN grades stiffen sharply in the cold and a seal that is rigid at start-up will leak before it warms.
- Keep bales off concrete floors and away from external walls to avoid moisture pickup, which causes porosity in the cured article.
- Provide extraction at mixing and curing, and control the compounding ingredients, which is where the occupational exposure in a rubber shop actually sits.
Hazard Summary
Classification: nitrile rubber in bale form is not classified as hazardous under CLP. The polymer is inert and is used in medical gloves and food-contact seals. Occupational risk arises from compounding ingredients and process fume.
Residual acrylonitrile: NBR is polymerised from acrylonitrile, which in monomer form is a Category 1B carcinogen and acutely toxic. Commercial polymer is stripped to very low residual levels and presents no practical exposure risk, but the figure belongs on the certificate and matters for food-contact, medical and glove applications where migration is assessed.
Poor ozone resistance: the butadiene double bonds that make NBR curable also make it vulnerable. A nitrile seal under strain in open air will crack, sometimes within months. This is a design consideration, not a storage one — antiozonant loading, a protective cover layer, or hydrogenated nitrile are the options.
Limited heat life: standard NBR is generally serviceable to around 100 °C continuous. Above that, ageing accelerates sharply and compression set rises. HNBR extends the range to roughly 150 °C, and above that the answer is a fluoroelastomer rather than a nitrile.
Cold stiffening at high ACN: a 50% acrylonitrile grade has a glass transition near −5 °C, so it is close to rigid at ordinary winter temperatures. Cold-start seal failures are a recurring consequence of specifying purely on oil resistance.
Compounding ingredients carry the hazard: carbon black, plasticisers, accelerators and antidegradants each have their own classification, and some accelerator classes have been associated with nitrosamine formation during vulcanisation. Assess the compound, not the polymer.
Fire: nitrile rubber burns readily once ignited, producing dense black smoke, carbon monoxide and, because of the nitrile groups, hydrogen cyanide and oxides of nitrogen. Fire response should assume toxic combustion products.
PPE minimum: gloves and safety footwear for bale handling; eye protection, gloves and respiratory protection appropriate to the compound at the mixer and press.
Consult the full SDS for the polymer and for every compounding ingredient before mixing.
Frequently Asked Questions
Technical and commercial questions about Nitrile Rubber (NBR) sourcing and specifications.
What is nitrile rubber used for?
Sealing against hydrocarbons is the core of it — O-rings, rotary shaft seals, gaskets and diaphragms in contact with mineral oil, hydraulic fluid and grease, where NBR is the default choice. Fuel and hydraulic hose liners are a large volume. Disposable gloves in carboxylated nitrile latex are now the largest single application by unit count. Beyond those, NBR goes into printing and industrial roll covers, oilfield components in hydrogenated form, and moulded industrial goods throughout automotive and machinery.
What does acrylonitrile content control?
Two things, in opposite directions, which is the central fact about specifying nitrile. Higher ACN means more polar nitrile groups, which makes the polymer less willing to absorb non-polar hydrocarbons — so oil and fuel resistance improve steadily as ACN rises from 18% to 50%. But those same polar groups increase intermolecular attraction and restrict chain motion, so the glass transition rises from around −40 °C at low ACN to roughly −5 °C at high ACN. A high-ACN compound that is superb in hot oil will be stiff and prone to leaking on a cold morning. Higher ACN also raises hardness, tensile strength and gas impermeability, and slightly reduces resilience. The correct grade is the lowest ACN that survives the fluid, not the highest available.
What is HNBR and when is it worth the premium?
Hydrogenated nitrile is standard NBR with most of its residual backbone double bonds hydrogenated away after polymerisation. Removing that unsaturation transforms the two weaknesses of nitrile: ozone resistance goes from poor to excellent, and continuous service temperature rises from around 100 °C to roughly 150 °C, with much better compression set retention. Oil resistance is unchanged, since the nitrile groups are untouched. It is worth the considerable price premium where a seal has to survive hot oil for years — automotive timing belts, air conditioning seals, and above all oilfield packers and stators in hot, sour downhole service where nothing cheaper survives.
Why did nitrile replace natural rubber in disposable gloves?
Primarily because of allergy. Natural rubber latex contains proteins that sensitise a proportion of people on repeated exposure, and healthcare workers wearing gloves all day were the most affected group — reactions ranged from contact dermatitis to anaphylaxis. Carboxylated nitrile latex contains no such proteins, so the sensitisation route disappears. It also happens to perform better for the job: nitrile resists oils, solvents and many chemicals that swell natural rubber, has better puncture resistance, and tears visibly when breached rather than developing an invisible hole. The switch was driven by health policy and then reinforced by performance.
What limits nitrile rubber?
Ozone and heat, both traceable to the same feature. The butadiene units leave double bonds in the backbone, and those double bonds are what sulphur crosslinks — but they are also what ozone attacks and what oxidises on ageing. A nitrile part held under strain in open air will develop ozone cracks, and continuous service above about 100 °C ages it rapidly. Compounding with antiozonants and antioxidants helps, protective cover layers help on hose, and hydrogenated nitrile removes the problem at a price. Nitrile is also unsuitable for polar fluids — brake fluid, ketones, esters and strong acids attack it, which is precisely where EPDM belongs instead.
What documentation does Chelora provide?
Every shipment includes a Certificate of Analysis covering acrylonitrile content, Mooney viscosity with test conditions stated, volatile matter, ash and coagulant type; a Safety Data Sheet to GHS and REACH format; REACH polymer compliance confirmation; antioxidant type declaration; residual monomer data and food-contact or medical documentation where the grade and application require it; an origin certificate; and destination-market certificates where required.
Request a quote or specification sheet
Talk to Chelora's sourcing team about Nitrile Rubber (NBR) grade, volume, logistics, documentation, and lead times. We respond within one business day.
